1. Field of the Invention
This invention relates, in general, to electrical apparatus and more specifically, to apparatus for externally controlling a secondary circuit breaker disposed within the tank of a distribution transformer.
2. Description of the Prior Art
Circuit breakers enclosed within a distribution transformer tank and connected to the secondary windings thereof have been used primarily to protect the distribution transformer from abnormally high load currents. Such breakers usually include means for opening and closing the circuit breaker and for resetting the circuit breaker after it has been tripped. Such circuit breakers also include an emergency overload adjustment or control which may be moved to change the tripping characteristics of the circuit breaker. That is, the emergency overload control may be moved to increase the amount of current which may pass through the circuit breaker before it is tripped. It is sometimes desirable to increase the rating of a circuit breaker under temporary conditions to prevent a power outage, even though the amount of power delivered by the distribution tranformer is greater than that for which it was primarily designed.
Distribution transformers equipped with secondary circuit breakers usually contain a signal light which provides an indication that the transformer has been moderately overloaded. When the transformer has been called upon to supply power above a predetermined level, the signal light is turned on and remains on until reset by a lineman. The signal light is turned on usually at a current output which is below the current output necessary to trip the breaker. Thus, such signal lights provide an indication of which transformers have been operating near the point at which circuit interruption may occur.
For various reasons, control of a circuit breaker is required from the outside of the transformer enclosure. When working on the secondary portion of the distribution system, it is often desirable to disconnect the transfromer by tripping the breaker. Thus, means located on the outside of the transformer tank is desirable to trip circuit breaker. Once the circuit breaker has been tripped, either purposely or by an overload current, it must be capable of being reset to reapply the power to the secondary distribution lines. Therefore, such a means located on the outside of the transformer tank is desirable. In addition, under temporary conditions, it may be desirable to increase the current carrying capacity of the circuit breaker from outside the transformer tank. Therefore, conventional control assemblies for distribution transformers having secondary circuit breakers include means located on the outside of the transformer tank for changing the value of current at which the breaker trips. This is usually accomplished by a mechanical adjustment on the bimetallic element used to trigger the circuit breaker.
A form of prior art control assembly for distribution transformers having secondary circuit breakers enclosed therein utilizes a control handle which are disposed around the signal light. Although the signal light and the control handle use only one opening in the transformer tank with such an arrangement, the complexity thereof and the cost of the die-cast components required thereby detracts from the economical benefits of such a combined device. In addition, it is difficult for these conventional assemblies to maintain an oil-tight seal between the inside and the outside of the transformer tank. Thus, it is desirable, and it is an object of this invention, to provide a control assembly for distribution transformers which is more economical, more reliable, and less complicated than previously used control assemblies for such transformers.